VEGETABLE CROPS

Fusarium Dry Rot of
Beans

Fact Sheet Page729.20 Date 11979

COOPERATIVE
EXTENSION  NEW YORK STATE  CORNELL UNIVERSITY

by
Arden Sherf Dept. of Plant Pathology Cornell University

Dry
root rot caused by the fungus Fusarium solani f. phaseoli directly
affects only the roots of the plants; however, the parts above ground are stunted
and may turn yellow, wilt, and die before the plants mature. If infection is only
moderate and rather general, the plants remain alive until harvest; but the whole
field will have the appearance of being undernourished as from a lack of nitrogen.
The plants may be affected as soon as they emerge from the ground; however, the
trouble is usually more common on older plants. When these are pulled, the side
roots are found to be rotted away and the tap root to have turned brick red and
become hollow and dry. New side shoots may have formed on the stem above the lesion.
Dry beans are affected more severely than snap beans.

The causal fungus
lives in bean refuse and also in the soil for several years. It grows into the
roots and up through the water ducts, thereby causing the plant to wilt. The fungus
rarely fruits before the infected stems or roots have started to decompose. The
spores and the mycelium are carried into the soil on tools and in bean straw manure.
They may also be splashed by rain or carried by floods. The fungus affects no
other crop. A Fusarium disease on peas looks very much like the one on beans,
but the two are distinct insofar as the hosts are concerned.

Control

When
putting into practice root rot control measures, one must remember that the pathogen
is not seedborne, but is strictly a soil organism. Because it is carried with
the bean straw, this should never be fed to animals, for the manure will carry
the organisms. The bean refuse should always be hauled where beans probably will
not be grown for 6 or more years. It is not known how long the root rot fungus
can live in the soil; but where a 6-year or longer rotation is practiced, the
disease is held in check sufficiently to grow a profitable crop. Where the usual
3-year rotation is practiced, root rot increases until finally bean growing in
those fields becomes impossible.

In addition to correct disposal of the
bean straw and long rotations, a few general recommendations can be made. Any
diseased bean refuse left on the field should be turned under deeply by fall plowing.
Beans should be planted only on well-drained, well-fertilized soil that is likely
to give an excellent growth of vines. Close cultivation should be avoided. If
the base of the plant rots off and new side shoots form above the lesion, the
plant may live if the newly formed roots are not cut off by the cultivator. The
more plant food and moisture available in the soil, the faster these side roots
will form, and the more chance there is for recovery and production of an acceptable,
although reduced, crop. Plant breeders are working to develop a variety resistant
to root rot.